1. Field of the Invention
The present invention relates to an image pickup device adapted for use in a video camera or the like.
2. Related Background Art
Recent remarkable progress in imaging equipment such as video cameras has realized automation of various functions and improvement in operability, such as incorporation of zoom lens, automatic focusing and automatic exposure control. For example, the automatic exposure control is an extremely important feature governing the quality of the obtained image, and has to always function stably and satisfactorily in any phototaking condition.
FIG. 1 is a block diagram showing a basic configuration of the exposure control system of an ordinary video camera, wherein provided are a phototaking optical system 101; an iris (diaphragm) 102 for regulating the amount of incident light; a photosensor device 103 such as a CCD, for effecting photoelectric conversion on an image, which is focused by the phototaking optical system on a phototaking face of the device and is regulated in the light amount by the iris, into an image signal; a camera signal processing circuit 104 for applying a predetermined signal processing to the image signal released from said photosensor device thereby obtaining a standardized image signal; an image signal output terminal 105; a motor 106 for driving the iris 102 for varying the aperture thereof; an iris driving circuit 107 for controlling the motor 106; a CCD drive circuit 108 for controlling the timing of accumulation, signal readout and resetting of the photosensor device 103 and varying the accumulation time (exposure time) of the device thereby obtaining a desired shutter speed; an automatic exposure control (AE) circuit 109 for evaluating the exposure state, based on the luminance signal from the camera signal processing circuit, and obtaining an optimum exposure by controlling the iris drive circuit 107 and the CCD drive circuit 108; and a switch panel 110 for entering key operations.
The exposure control by the AE circuit 109 is conducted in the following manner. There is formed an iris controlling closed loop, for integrating the luminance signal from the signal processing circuit 104, controlling the iris driving circuit 107 so as to maintain the level of said signal within a predetermined range and controlling the drive current to the iris motor for varying the aperture of the iris, and there is provided a control system for controlling the CCD drive circuit 108 to switch the driving pulses thereof in response to the key operation on the switch panel 110, thereby varying the accumulation time of the image pickup device 103 to control the exposure time and to obtain an appropriate exposure. The accumulation time control is called electronic shutter, and can select several stages from {fraction (1/100)} sec. to {fraction (1/10000)} sec., in addition to the ordinary exposure time of {fraction (1/60)} sec. for NTSC standard.
When a high-speed electronic shutter is used in such system, there is assumed so-called shutter priority mode in which the iris is controlled according to an arbitrarily selected shutter speed. FIG. 2 shows said shutter priority mode, in which the shutter speed in the abscissa is at first fixed, and the aperture value in the ordinate is varied accordingly.
However, the above-explained iris control in the shutter priority mode according to the luminance level of the image signal as in the foregoing video camera is unable to provide appropriate exposure control under various phototaking conditions.
In a camera for still image taking, such as a conventional still camera utilizing a silver halide film, the exposure control needs to be appropriate only at the moment of phototaking, but, in case of recording the moving image for a long time as in the video camera, the exposure control has to be conducted in constantly stable and optimum manner, following the continuously varying conditions in the course of phototaking operation, and an exposure control device for video camera, meeting these requirements, has been longed for.
In consideration of the foregoing, a first object of the present invention is to provide an image pickup device for a video camera always capable of optimum exposure control, regardless of the situation or condition of phototaking.
A second object of the present invention is to provide a video camera capable of always setting an optimum exposure control mode, according to the phototaking situation.
A third object of the present invention is to provide a video camera capable of selecting the phototaking modes according to the phototaking circumstances.
The above-mentioned objects can be attained, according to a preferred embodiment of the present invention, by an image pickup device capable of effecting exposure control with plural control parameters, comprising means for setting a light metering area in the image frame, means for setting an input parameter, based on the luminance information contained in an image signal obtained from said light metering area, means for determining the values of plural control parameters used for exposure control, according to the value of said input parameter, switch means for switching the control parameters relative to said input parameter, according to the phototaking mode, and photometry area switch means for switching the set state of the photometry area in said image frame.
It is therefore rendered possible to set plural control parameters and to control said parameters and the photometry area according to the phototaking conditions, thereby achieving optimum phototaking operation constantly in any phototaking situation or circumstances.
Also according to a preferred embodiment of the present invention, there is disclosed an image pickup device capable of effecting exposure control with plural control parameters, comprising means for setting an input parameter, serving as a reference for evaluation, based on the luminance information obtained from the image signal, means for determining the control parameter used for exposure control, from the iris aperture, shutter speed and gain of AGC circuit, according to the value of the input parameter, at least two data memory means storing the control characteristics of the control parameters corresponding to the input parameter, and selection means for arbitrarily selecting either of the data memory means.
A fourth object of the present invention is to provide an image pickup device constantly capable of optimum exposure control in any phototaking situations such as portrait, indoor phototaking, landscape phototaking, high-speed object (sports) phototaking, snowed landscape phototaking, beach phototaking, full automatic mode, manual phototaking mode etc.
A fifth object of the present invention is to provide an image pickup device capable of optimum exposure control by varying the phototaking mode through combination of plural control parameters and switching the photometry area in response to a change in the phototaking mode.
A sixth object of the present invention is to provide a video camera capable of varying the shutter speed, iris aperture, gain and photometry area, thereby effecting different controls, in plural phototaking modes corresponding to plural phototaking situations.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description, which is to be taken in conjunction with the attached drawings.